Electrode for electron discharge devices



NAG NET! C TBANSFOBHA T/ON C02 V5 :avme farm i l 10 PIRCENTAE 0E COBALT IN ALLOY Dec. 20, 1938. .c H. MAH ONEY ELECTRODE FOR ELECTRON DISCHARGE DEVICES Fil'ed Jan. 11, 1957 amen-s 17. JVAHO/VEV.

haunted Dec. 2c, 1938 2,140,534

(",UNITED STATES PATENT OFFICE ELECTRODE FOR ELECTRON DISCHARGE DEVICES Charles H. Mahoney, Owensboro, Ky., assignor to The Ken-Rad Tube and Lamp Corporation, .Owensboro, Ky., a. corporationof Kentucky Application January 11, 1937, Serial No. 119,928 2 Claims. (Cl. 250---27.5)

} fI'his invention relates to electrodes for electron surface for the coating of the electron emissive discharge devices, and more particularly to magsubstance. Those skilled in the ,art will readily netically shielded electrodes constructed in a appreciate that an irregular coating of the elecnovel manner and including an improved alloy tron emissive substance is readily chipped, therehaving a high magnetic permeability at high after rendering the discharge device unsatisfactemperatures. tory. It is thus an object of this invention to With the advent of indirectly heated cathodes provide a novel seamless tube cathode construcand the use of alternating current electricity as a tion for electron discharge devices.

source of heat for raising the temperature of a It is a further object of this invention to prono cathode to its desired electron emission point, a vide a novel seamless tube cathode having a 10 newproblem presented itself to the radio enlayer of ferrous-cobalt alloy and a superimposed gineer. It was found that the current flowing layer of some other metal.

through the heating element set up an electro- Another and further object of this invention is magnetic field which reached out into the region is to provide a novel cathode construction includof normal electron flow. This electro-magnetic ing a seamless tube of ferrous-cobalt alloy and a field thus influenced the electrons emanating second tube of non-ferrous metal disposed over from the cathodes and thereby caused undesir the alloy tube, there being a welded bond thereable fluctuations of current in the anode circuit between.

of the discharge device. Many suggestions have Another and further object of this invention is I been proposed to overcome the'eifect of this electo provide a novel cathode construction including 20 bro-magnetic field, such for example, as by ema tube of ferrous-cobalt-nickel alloy.

ploying a heating element having a resistance The novel features which I believe to be charwire which is wound in a reverse helical manner, acteristic of my invention are set forth with parthe'. assumption being that the oppositely directed ticularity in the appended claims. My invention .25 magnetic fields developed bytheneighboring secitself, however, both as to its composition and ftions ofa heatingwire would cancel each other. manner of construction, together with further It has been found, however, that the more efobjects and advantages thereof, may best be unfective way of eliminating the undesirable efderstood by reference to the following descripfects of this magnetic field is to construct the tion taken in connection with the accompanying 13o cathodes with an inner shield composed of a madrawing in which:

. te'rial having a high magnetic permeability at Figure l is an elevational view partly in crossb high temperatures which will substantially presection, but not drawn to scale for purposes of vent the electro-magnetic field referred to above clarity, of an electron discharge device;

from extending beyond the shield. Figure 2 is a cross-sectional end view of the Thus itis an object of this invention to procathode of the electron discharge device illus- 5 videa novel shielded electrode construction. trated in Figure 1; and

' It is a further object of this inventionto pro- Figure 3 is a diagram illustrating the magnetic vide an electrode having a shielding layer of transformation characteristic of the shielding novel composition. material employed in the construction of the 4g It is a still further object of this invention to cathode illustrated in Figures 1 and 2. 40

provide a cathode having a layer of ferrous-co- In Figure 1 of the drawing, an electron disbait alloy, the cobalt content being sufficient to charge device 10 is illustrated and includes a provide a stable magnetic transformation charcathode heating coil H, a cylindrical cathode l2, acteristic. g a grid electrode I3, and a plate electrode or anode .45 It is a still further object ofthis invention to it. Although discharge device of Fig. 1 is shown provide a cathode having a layer of ferrous-co- 'as being provided with a single grid electrode, it ball) y, the cobalt content being at least is to be understood that the device may be pro- Now in the construction of duo-metal article's, vided with any number of grid electrodes or it is, of course, easier to manufacture them in without any grid electrodes without departing 59 sheets or strips and then form the desired article from the spirit and scope of this invention.

thereafter. Tubing composed of metal such as Now the particular construction of cathode 12 all ys vin a f r us-c a o p h w- (see Figures 1 and 2) constitutes one of the cardiever, cannot be readily welded,and tubing which nal features of the present invention, and includes has been formed with a locked seam or the like an inner'layer l5, composed of a novel ferrous- 'is objectionable in that it presents an irregular cobalt alloy having a high magnetic permeability 55 characteristic at high temperatures. As will be presently pointed out this layer l5 prevents the electro-magnetic field set up by the flow of current through heating coil H from extending'into the region of normal electron flow which exists in the space l6 between cathode l2 and anode I4. As is the common practice in the construction of electron discharge devices of the indirectly heated cathode type, cathode l2 includes an outer layer l! of some suitable electron emissive substance, such as an oxide of the alkaline earth group. In order to prevent any chemical reaction between layer 11 and the ferrous-cobalt alloy layer IS, a layer iii of non-ferrous metal such as nickel or copper is interposed between the electron emissive substance I! and the ferrous cobalt alloy [5. Preferably, this metal should be a good conductor'of electricity, non-reactive chemically to the electron emissive substance, and have good adhesion properties with respect to the electron emissive substance. I

It has been found that when inner layer [5 of cathode I 2 is constructed from a ferrous-cobalt alloy having a certain predetermined minimum percentage of cobalt therein, a very effective magnetic shield is obtained. In Figure 3 of the drawing, the magnetic transformation curve M of ferrous-cobalt alloys is illustrated. The percentage of cobalt in the alloy is plotted as the abscissae of the curve while the temperatures at which the Curie point or magnetic transformation takes place is plottedas the ordinates of the curve. Upon inspection of Figure 3 of the drawing, it will be noted that the left hand portion of the curve M is dividedinto two portions M1 and M2. The region B between zero percentage of cobalt and approximately 21% cobalt constitutes an unstable transformation region. Since the usual maximum temperature at which the cathode of an electron discharge device operates is approximately 900, it has been found important to have a cobalt content in the alloysufiicient to cause operation along or near the stable portion of the magnetic transformation curve M. That is to say,

r' it is desirable to have at least 19% cobalt content One extremely satisfactory method of forminga ferrous cobalt alloy such as that described above into a seamless tube cathode structure I2 is to first hot or cold draw a tube of ferrous Cohan;

alloy to within two or three of the final passes, and then electroplate a metal such as nickel thereon. The plated tubing is then redrawn to effect a welded bond between the ferrous-cobalt alloy and the nickel plating. After this hot or cold work ing operation, the tubing is again electroplated with nickel and then redrawn until the desired tube size and coating thickness are obtained. Thereafter, a coating of .an electron emissive substance such as oneof the oxides of the alkaline earth group may be applied to the outer surface of the nickel in the conventional manner. bonding of the plated tubing substantially eliminates blistering of the nickel on the alloy.

A second satisfactory method of constructing a This seamless tube cathode having an inner layer of ferrous-cobalt alloy includes hot or cold drawing a tube of ferrous-cobalt alloy to approximately its desired final size. A pre-drawn tube of nickel having an inside diameter substantially the same as the outside diameter of the drawn ferrouscobalt alloy tube is then slipped or forced over the latter. This assembly is then'hot or cold drawn to size to effect a welded bond between the two metals. Thereafter a coating of an electron emissive substance such as one of'the oxides of the alkaline earth group is applied to the outer surface of the nickel in the conventional manner.-

Although the relative dimensions of the respective layers of the cathode may vary through wide ranges without departing from the spirit and scope of this invention, the only purpose of the nickel layer is to function as a chemical shield between the ferrous-cobalt alloy and the emissive coating. Now the magnetic shielding effect of the ferrous cobalt alloy increases with the wall thickness. Therefore, it is desirable that the nickel obtaining of a continuous chemical shield so-that as much of the total wall thickness as is possible will be available for the magnetic shielding alloy. It is desirable to keep the combined cathode Wall thickness as thin as possible for the following reasons: a

1. For ease of degasification of material. .2. To facilitate quick heating.

3. As space conservation for heater.

(Usually in practice it'ranges from .001 to .005).

Although I have described nickel as being electrolytically deposited on a ferrous cobalt alloy, it is to be understood that the process may be reversed and the ferrous cobalt alloy electrolytically deposited on the nickel without departing from the spirit and scope of this invention.

While I have described particular. embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I therefore contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my inventions 1. A laminated cathode for electron discharge devices comprising an innerlayer of magnetic shielding material composed of a malleable ferrous-c'obalt alloy having acobalt content of at least 19% and a ferrous content of aproximately to an outer layer of an electron-emissive surface, and an intermediate layer of a nonferrous metal of good electrical conductivity to prevent chemical reaction between said outer wall be made as thin as is commensurate with the layer and said inner layer, said intermediate CHARLES H. MAI-IONEY. 

